1. FIELD OF THE INVENTION
The present Invention relates to apparatus and method For recognizing head position information, and apparatus and method for head positioning that are necessary when a data-head Is moved to an arbitrary track containing information on a rotatable recording medium.
2. DESCRIPTION OF THE PRIOR ART
Heretofore, in a magnetic disk apparatus, dedicated servo-control method; has been employed widely wherein, a data head can achieve the positioning action toward the destination data track, by being guided by servo information written a surface of a layered recording medium. In this scheme, however, the positioning of the data head is performed on the assumption that the relation between the servo surface and the data surface is definitive and reliable one. Consequently, there has been a drawback that off-tracks were apt to happen due to various circumstantial variations such as temperature change inside the apparatus housing and hence it was substantially difficult to attain a high packing track density.
Then, in recent years, much attention has been given on the data-plane servo schemes in that the servo information was written over the data plane and thereby the reliability at the time of recording-reproduction action was improved.
As one of those schemes, the sector-servo scheme has been proposed. In this scheme, at every leading part of respective sector, positioning servo-sector has been (i.e. preliminarily written in) buried in. Then, when an arbitrary data track is selected, a head is servo-tracked to a destination track based on the servo information of the servo-sectors,. However, in this scheme, only the information necessary for tracking control is provided. Therefore, it was a drawback that, in order to let the head move radially at high velocity, an extra positioning detector besides a data head must be provided, or head position information must be supplied from the servo plane. Also, when it is intended to obtain sufficient position information to obtain even at the time of high velocity access only by the servo information of the servo-sector, the ratio of occupation from servo-sectors in the area of a recording medium necessarily increases. This induces a problem of resultant reduction of an available memory capacity in a given recording medium.
Then, it is proposed to code and record the track numbers within the servo-sectors to perform the head access action basing on these recorded informations (Japanese published unexamined patent application=Tokkai Sho 51-131607). In this scheme, by obtaining discretely the position information (address Information) of the track over which the head passes during the time of its seek action, average velocity between sectors is obtained, and by comparing this with an instructed velocity, the velocity control is accomplished. Thus this scheme is simple in its mechanics and has good cost performance even case of having small number of laminated recording media, and hence it is widely being used. However, the above-mentioned scheme in which the track numbers are recorded by coding them in the servo-sectors on the recording medium plane (The Tokkai Sho 51-131607), there was a problem that only one code is allotted to each data track. Therefore, the track position information obtainable from each servo-sector includes errors as large as one-track width at maximum. Therefore, the error in detection of velocity, i.e., velocity detection error .DELTA.V can be expressed by ##EQU1## where Xtp is the track pitch and Ts is the time necessary for passing one servo-sector pitch. .DELTA.V corresponds to several cm/s. Generally, In the transient state switching from the seek action to the tracking control action, in order to make a stable radial moving and landing, a sufficient control of the moving velocity of a head to about several cm/s is necessary. However, under the situation that the velocity detection error is existing as much as several cm/s, sufficient control of the moving velocity control is difficult. As a result, the head can land on the destination track after repeating large overshoots and undershoots therearound, requiring a considerable time until reaching a final setting. At the worst case, a seek error takes place and could crash the disk. That is, accuracy of the head position detection at the time of seek action has been a problem to be attacked for improving the total performance of the head positioning apparatus.
For the above-mentioned coding of the track number, as the recording density on a recording medium has been improved, the number of the Information tracks also increases, and hence a large area becomes necessary. That is, the ratio of occupation of servo region with respect to the data region on a recording medium increases, hence giving rise a problem that the maintaining of a large capacity is becoming difficult.